The subject invention relates to an atmospheric wind measuring apparatus utilizing acoustic beams, and more specifically, to a monostatic system with a fixed array of acoustic transducer elements.
Doppler acoustic systems are used to measure atmospheric winds remotely from a site on the ground. Valid measurements are obtained typically to heights of many hundreds of meters, occasionally to well over a kilometer. Such instruments are therefore of considerable value in obtaining continuous wind profiles for use in connection with pollution monitoring, wind power, meteorology, atmospheric modeling and other applications.
A full description of the wind vector at a given location and time requires the determination of three components. These are frequently taken to be the east, north and vertical components. Different component resolutions, e.g., speed, direction and vertical, are equivalent, and each set can be readily converted to the other.
On configuration of a doppler acoustic system for measurement of wind velocity and direction is shown in U.S. Pat. No. 3,889,533. This is a bistatic system with a transmitter and two or three receivers spaced from the transmitter. Typically the transmitter directs a beam vertically upward and the receivers provide a measure of scattering at various elevations along the beam. The receiver outputs are processed to provide a velocity vector indicating wind velocity and direction.
Another configuration of a doppler acoustic system that measures three independent components of wind is the monostatic system, i.e., one in which the same antenna serves as transmitter and receiver of the acoustic energy. FIG. 1 shows schematically how this is normally accomplished.
Three different antennas 11, 12, 13 are employed, each generating one beam to measure one of the three wind components. The beam of antenna 13 points vertically, the beam of antenna 11 points towards the east, and the beam from antenna 12 toward the north, the latter two at some angle .gamma. from the vertical. The details of pointing angles are not critical; any set of three independent measurements can be converted to the desired wind components. Most commonly, each antenna consists of a reflecting dish, on the order of 1 meter in diameter, irradiated by an acoustic driver, or possibly a small cluster of drivers.
Such systems suffer from two limiting disadvantages. First, the three antennas with their acoustic shields are very large and bulky, and require considerable effort to move and align. Second, the radiated power available from a single acoustic driver limits the range (altitude) from which usable returns are obtained.
A monostatic system using four antennas, each comprising an array of drivers or acoustic transducer elements in the form of commercial loud speakers is shown in U.S. Pat. No. 3,675,191. The beams from the four antennas are fixed in direction, with the return signals from the four antennas being mixed in various combinations to provide the desired output.
It is an object of the present invention to provide a new and improved acoustic wind velocity measuring system utilizing only a single antenna having an array of acoustic transducer elements or drivers. This provides a significant advantage over prior art systems in that the size, cost and weight of the antenna arrays is a significant factor in manufacture, installation and operation of wind measuring systems.
It is a further object of the invention to provide such a system which can provide beams of acoustic energy at three different predetermined angles from a single antenna for transmitting acoustic energy along three different paths and receiving the transmitted energy as scattered by wind in the paths, with the received energy being converted to electrical signals for processing to provide the wind velocity vector. An additional object of the invention is to provide such a system wherein the three beams are produced in sequence by controlling the phase of the driving input to the individual elements of the antenna array.
It is a particular object of the invention to provide such a system wherein the desired beam paths and wind velocity information can be achieved while requiring only a single 90.degree. phase shift in the driving signals.
Other objects, advantages, features and results will appear in the course of the following description.